1. Field of the Invention
The present invention relates to an improvement in a friction plate and a multi-plate clutch using such friction plate, which are used as friction plates or a lock-up clutch in a wet type multi-plate friction engaging apparatus having a plurality of friction plates and used in an automatic transmission of a motor vehicle or a transmission of a motor bike.
2. Related Background Art
In the past, a friction plate was manufactured by adhering a plurality of friction material segments onto an annular core plate in a circular pattern. For example, as shown in FIG. 5, the friction material members were interconnected through a connection portion like a configuration of a piece of jigsaw puzzle.
In FIG. 5, a friction plate 21 is obtained by assembling three friction material segments 22 in a circular pattern and adhering these segments onto a core plate 23. Each friction material segment 22 has is provided at its both ends with a connecting portion 25 including a projection and a recess, and the adjacent friction material segments are interconnected by engaging with the connecting portions together. Further, the core plate 23 is provided at its inner periphery with splines 24 for connecting to a rotary shaft or the like (not shown).
However, when the friction material segment is manufactured by punching it from a friction material tape, burr can be generated at an edge of the punched friction material segment. Further, since adjacent sections (connection portions) between the friction material segments have weaker strength in comparison with the other part of the segment, when an engaging operation is repeated by numerous times, the adjacent section can be peeled or broken.
Therefore, an object of the present invention is to prevent an adjacent section of a friction material segment from being peeled or broken.
To achieve the above object, the present invention provides a friction plate obtained by adhering a plurality of friction material segments onto a core plate, wherein an axial thickness of the friction material segment in areas including adjacent portions between the adjacent friction material segments is thinner than the other portion of the friction material segment.
Further, to achieve the above object, the present invention provides a multi-plate clutch comprising a clutch case and a hub which are rotated relative to each other on the same axis, separator plates disposed on an inner periphery of the clutch case, friction plates disposed on an outer periphery of the hub and arranged alternately with the separator plates in an axial direction, and a piston for urging the separator plates and the friction plates to frictionally engaged the plates with each other, and in which input and output of a driving force is effected between the clutch case and the hub, and wherein each of the friction plates is formed by adhering a plurality of friction material segments to a core plate, and an axial thickness of the friction material segment in areas including adjacent portions between the adjacent friction material segments is thinner than the other portion of the friction material segment.
The friction plate according to an embodiment of the present invention is formed by providing areas each having a thickness thinner than that of the other portion at the adjacent portions of the friction material segment of the above-mentioned conventional friction plate. Such an area includes all shapes including the adjacent portions between the friction material segments and is not limited to a specific shape. Further, a depth of the area is not particularly limited and may be any depth so long as the area is slightly lower than a friction engaging surface of the friction plate.
The area is desirably formed by pressurization and compression, since strength of a boundary between the area and a portion other than the area can be maintained and the formation of the area can easily be achieved for a short time.